What role does Dicer play in RNA interference?

Dicer plays a crucial role in the RNA interference (RNAi) pathway by processing double-stranded RNA into small interfering RNAs (siRNAs). This is a key step in the gene silencing process. Dicer recognizes and binds to double-stranded RNA, which can originate from exogenous sources such as viral RNA or from endogenous sources like long double-stranded RNA transcripts. It then cleaves this double-stranded RNA into shorter fragments, typically around 21-23 nucleotides in length.

These siRNAs are then incorporated into the RNA-induced silencing complex (RISC), where they guide the complex to complementary mRNA targets, leading to the degradation of the mRNA and subsequent suppression of gene expression. The production of siRNAs by Dicer is fundamental to the effective functioning of RNA interference, enabling the cell to regulate gene expression and defend against viral infections, highlighting the importance of Dicer in post-transcriptional regulation.

Other options do not align with Dicer's function in RNA interference. For example, synthesizing mRNA from DNA involves RNA polymerases, while ribosome assembly is facilitated by different factors and histone modification pertains to chromatin structure and gene regulation rather than RNA processing.